We have defined an HLA locus (SB) which maps centromeric to the other known genes of the HLA complex. We are analyzing the importance of the genetic region marked by this gene in human disease. Family studies are continuing in dermatitis herpetiformis and are confirming the concept that the SB1 allele is part of an entire HLA haplotype which occurs in increased frequency in affected individuals. Studies have been initiated on juvenile rheumatoid arthritis, specifically patients with the DR5 allele, in order to determine whether there is an extended HLA haplotype (including an SB allele) which confers disease susceptibility. Finally, a study has been started in bone marrow donor-recipient pairs in order to: a) identify additional SB/DR recombinant individuals; and b) determine if SB-mismatching between otherwise HLA-identical donor-recipient pairs predisposes to morbidity or mortality.